Fixes #4374 - Nukes all (?) legacy Driver and Application stuff; revamps tests (#4376)

Tests/UnitTests/Application/SessionTokenTests.cs

@@ -0,0 +1,79 @@
+
+namespace UnitTests.ApplicationTests;
+
+/// <summary>These tests focus on Application.SessionToken and the various ways it can be changed.</summary>
+public class SessionTokenTests
+{
+    public SessionTokenTests ()
+    {
+#if DEBUG_IDISPOSABLE
+        View.EnableDebugIDisposableAsserts = true;
+
+        View.Instances.Clear ();
+        SessionToken.Instances.Clear ();
+#endif
+    }
+
+    [Fact]
+    [AutoInitShutdown]
+    public void Begin_End_Cleans_Up_SessionToken ()
+    {
+        // Test null Toplevel
+        Assert.Throws<ArgumentNullException> (() => Application.Begin (null));
+
+        var top = new Toplevel ();
+        SessionToken rs = Application.Begin (top);
+        Assert.NotNull (rs);
+        Application.End (rs);
+
+        Assert.NotNull (Application.Top);
+
+        // v2 does not use main loop, it uses MainLoop<T> and its internal
+        //Assert.NotNull (Application.MainLoop);
+        Assert.NotNull (Application.Driver);
+
+        top.Dispose ();
+
+#if DEBUG_IDISPOSABLE
+        Assert.True (rs.WasDisposed);
+#endif
+    }
+
+    [Fact]
+    public void Dispose_Cleans_Up_SessionToken ()
+    {
+        var rs = new SessionToken (null);
+        Assert.NotNull (rs);
+
+        // Should not throw because Toplevel was null
+        rs.Dispose ();
+#if DEBUG_IDISPOSABLE
+        Assert.True (rs.WasDisposed);
+#endif
+        var top = new Toplevel ();
+        rs = new (top);
+        Assert.NotNull (rs);
+
+        // Should throw because Toplevel was not cleaned up
+        Assert.Throws<InvalidOperationException> (() => rs.Dispose ());
+
+        rs.Toplevel.Dispose ();
+        rs.Toplevel = null;
+        rs.Dispose ();
+#if DEBUG_IDISPOSABLE
+        Assert.True (rs.WasDisposed);
+        Assert.True (top.WasDisposed);
+#endif
+    }
+
+    [Fact]
+    public void New_Creates_SessionToken ()
+    {
+        var rs = new SessionToken (null);
+        Assert.Null (rs.Toplevel);
+
+        var top = new Toplevel ();
+        rs = new (top);
+        Assert.Equal (top, rs.Toplevel);
+    }
+}